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Expert: Thomas Date: 7/15/2008 Subject: color variation on sandblasted gold coins
Question Thomas -
There is debate among numismatists regarding the colors seen on the very rare (and expensive) gold coins sandblasted by the US Mint in 1907-1915. I'm hoping you can help us demystify the subject.
Typically, sandblasted coins of a given year have a distinctive color, clearly different than coins of other years. When the coins are treated with solvents, the distinctive colors are minimized or eliminated, so that all of the coins look more or less the same. This much is uncontested.
The questions are, what are the possible causes of the color variation? Is the solvent removing a Mint-applied finish? If so, what exactly is being removed?
Thank you!
Answer Andy, I am back. And, I do ask a favor of you regarding "rating the expert". I have told you I am not a coin person and honestly know very little about coinage. I took on the question because it is intriguing and I hoped to learn a little myself in trying to find an answer. With this in mind, I would normally reject a question almost totally out of my field but this one was different. So, please do not feel any need to rate the answer. I start off with admitted little knowledge in the area of your question but will tell you my thoughts on the situations with the matte coins.
As I understand it, the coins were struck with a die which was either acid etched or sandblasted. The die transferred the matte finish to the coins. As for solvents, solvents are made for applied finishes such as lacquers, acrylics, etc. I cannot imagine any reason for the mint to apply a finish to the coins. It makes little sense to coat for a coin aimed for collectors as a matte proof.
What can change is coins is the “exact alloy of gold” used for the coin. Can we say the alloy is exactly the same each year? Possibly but with certainty? Were any of these coins struck in the Middle East and processed through the U.S. Mint? Who controlled the exact metal mix in the coinage blanks? Yes, we can say what percent or FINENESS of gold the coins contain but what about the other metal in the mix?
Why would I ask this question in the first place? This is why: Tarnish. Depending on the exact alloy mix of gold, even if all of the same fine gold content, tarnish reactions can differ. Coins stored in cardboard may be exposed to compounds from the papers which over time lead to tarnish. The sort of cardboard may even vary from year to year and some may be worse for causing tarnish than others. My thought is tarnish, even of the slightest amount which even high karat gold may develop. This will certainly change the color slightly.
If the solvents are coin dealer approved methods of tarnish removal, when the tarnish is gone and the coin look pristine and untouched, the actual colors of the coinage should be very close to the same for each year. In this case, the cleaning is not actually by solvents but by other chemical processes. Frankly, considering the value of the matte proof coins, I would hesitate to do any attempt to clean the coin. Perhaps what you speak of is an accepted practice which does not affect the value or touch the gold except for very gentle tarnish removal.
Andy, this is my thought. I may be totally off base. As it seems, with numismatist debating the issue I am not alone.
Thanks for the very interesting question and my intro to matte proof gold coins.
God Bless and Peace. Thomas. July 16, 2008 7:03pm
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Andy, this is not your answer but a prologue, as it may. I am certainly not a numismatist and know little of this color variation. I have not seen a sandblasted coin and would assume if I saw one it was done by some individual, not the mint. You have given me new knowledge and something to truly consider.
This is what I will do: Give me a day to consider what you have said. I already have a few thoughts on the question. Then, tomorrow evening I will write and send an answer to you. Well, Andy, tomorrow evening I will send my thoughts to you, likely not a true answer. : )
In the meantime, is there a chance you can use the follow-up and perhaps let me know what sorts of solvents are used on the coin? The type of solvent will take the question from gold and chemicals to gold and applied finishes. I am familiar with these subjects.
Thanks again. I do hope you get the chance to get back.
